Paraphrasing Dershowitz' own words taken from The Hill: Media pundits and partisan politicians have been deliberately distorting the argument, as if I claimed a president who believes his reelection is in the national interest can do anything. I said "nothing like that." Responding to House managers, I said any action by a politician motivated by a desire to be reelected was, by its nature, corrupt. Dershowitz listed three broad categories of relevant motive: pure national interest to help the military; pure corrupt motive to obtain a kickback; mixed motive to help national interest in a way that can also help a reelection effort.
The third motive was the reality of politics and helping your reelection cannot "by itself" be deemed corrupt. Example: Hypothetically, President Obama promised to bomb Syrian military targets if Assad used chemical weapons, but broke that promise. If Obama stopped the bombing because advisers warned it would lose him votes; the framers of the Constitution did not intend impeachment for "mixed motives" decisions that contain an element of personal partisan benefit. House managers claimed that "any" electoral benefit constitutes a quid pro quo and how open ended that argument is, since most politicians believe their reelection helps national interest. Dershowitz never said a candidate could do anything to assure their reelection!
Dershowitz said those talking heads who mischaracterized my argument knew what they were doing. Instead of responding to the Obama example, they decided to create a false narrative which they could mock! My point was that if a president does something within his authority like pausing aid, sending soldiers home, not bombing Syrian military targets, the fact he was motivated in part by reelection does not in itself constitute impeachable conduct.
Under this motivation theory, Joe Biden would be guilty, even if a small part of his motivation was protecting his son or his company as he was not running for reelection. Under this dangerous theory of House managers, people would have to be psychoanalyzed to determine the role each motive played and takes the country down a very dangerous road.
Mixed motives are always matters of degree and if they become criteria for impeachment, they can be used selectively against certain candidates and not others. This deliberate distortion is a symptom of our times and creates a divisive America.